"track to" object under "parent" constraint
As I understand your problem here the my solution.

Try to do this setup from different way.


Add a "rotation" bone, witch will control hole system in z rotation.


next setup "camera direction" bone, lock its moving in x axis and parent it to the "rotation" bone. I use IK in both cases.


When you just need to setup your bones with correct lengths and axis locks. On last bone make IK constraint to the "camera direction" bone with rotation option enabled